Control system



June 8, 1948. EDWARDS 2,443,028

CONTROL SYSTEM Ofiginal Filed March 21, 1936 Inventor: Martin A.Edwards,

H is Attorneggderstand that the power shaft l9 driven by the motor 22drives a variable stroke oil pump, which supplies a variable volume ofoil to a fluid motor which drives the output shaft 2|. The amount of oilsupplied to the fluid motor is determined by the position of the controlelement 20, which when rotated varies the stroke of the oil pump. Vhenno oil is supplied to the oil motor, the output shaft 2| is at rest, andwhen a maximum amount is supplied, the shaft 2| rotates at maximumspeed. Similarly, for intermediate rates of oil supply, the shaft 2|rotates at corresponding speed. The direction of rotation of the outputshaft 2| depends upon the direction in which the control shaft 20 isturned from its neutral position.

The control shaft 20 is actuated through suitable differential gearing2'! whose input spider 21a is geared to the input shaft I8. One bevelgear 28 of the differential device is connected through gearing 29 tothe output shaft 21 and another bevel gear 30 is connected as shown,through gearing connections to the control element 20. With the powerinput motor 22 driving the power shaft l9 at full speed and with thecontrol element 20 in its neutral position, the pump will have zerostroke and under this condition, the output shaft 2| will be at rest.When the motor 24 first begins to turn, the input shaft l8 does not havesufficient torque to move the heavy load l3, so it turns the controlshaft 2!! instead, thereby opening the throttle some definite amount. Asa result of the rotation of the control shaft, the output shaft wouldbegin to rotate and continue to rotate at a speed proportional to thenumber of rotations of the control shaft, if it were not for the factthat the output shaft is connected back through the differential device21 to the control shaft, so that when the output shaft is rotated, itturns the control shaft backwards toward its initial neutral position.As the control shaft is turned backward, the speed of the output shaftis of course diminished and when the control shaft is returned to itsinitial position, the output shaft is stopped. Thus, it will be seenthat with the differential gear 2'! connecting the output shaft and thecontrol shaft, the transmission device [4 functions inherently as afollow-up device, and the number of rotations of the output shaft 2!correspond exactly to the number of rotations of the input shaft It in aproportion depending upon the ratio of the gearing 29. However, if theinput shaft is is rotated continuously, the output shaft 2| will alsorotate continuously and at a corresponding velocity, but it will la theinput shaft by an amount proportional to the velocity of the outputshaft.

The electric valve apparatus 26 comprises a pair of valves 26a forsupplying current in one direction to the armature of the pilot motor 24and a second pair of valves 26b for supplying direct current to thearmature in the reverse direction. These valves are in turn. suppliedfrom a suitable source of alternating voltage represented by the threesupply lines 3| through a suitable supply transformer 32, the primarywinding of which is connected to the upper and middle supply lines 3!and the secondary windings of which are connected to the anodes of thefour valves as illustrated. Thus, each pair of valves is connected forfull wave rectification.

Although the electric valves may be of any suitable type, they arepreferably of the threeelectrode type having a small quantity of aninert gas introduced into the envelope after exhaust. This inert gas maybe mercury vapor or any other suitable gas and it serves to convert theusual pure electronic discharge into an arc stream there by constitutingthe valve a grid controlled arc rectifier. The average value of thecurrent flowing in the anode circuit of electric valves of thischaracter can be controlled by varying the phase relationship betweenthe voltages supplied to the grids and the anodes respectively. When thegrid voltage is substantially in phase with the anode voltage, thecurrent flowing'in the anode circuit is maximum and when the gridvoltage is lagging with respect to the anode voltage by a predeterminedamount, usually more than the current flowing in the anode circuit is aminimum or substantially zero. For intermediate values of phaserelationship between these voltages, the current how has correspondingintermediate values.

Alternating voltage is supplied to the grids of electric valves 26a and26b by means of grid transformers 33 and 34 respectively, whose primarywindings are connected in series relationship with the secondary windingof a grid biasing transformer 35. One of the terminals of the primarywinding of the grid biasing transformer is connected to an intermediatetap of the primary winding of the supply transformer 32 and the otherterminal is connected to the lower supply line 3!. This connection ofthe primary winding of the biasing transformer serves to derive avoltage for the grid or input circuit of the electric valve apparatuswhich is more than 90 lagging with respect to the anode voltage so thatboth pairs of valves are normally held at out off and therefore supplyno current to the armature of the motor 24.

For the purpose of varying the phase relationship between the grid andanode voltages, a component voltage is supplied to the grid or inputcircuit through a transformer 36, one of whose secondary windingterminals is connected to an intermediate point of the secondary windingof the biasing transformer 35 and whose opposite terminal is connectedto the common point between the primary windings of the gridtransformers 33 and 34. Whenever this component voltage is present, itis substantially in phase with the anode voltage of one of the pairs ofvalves and, therefore, substantially out of phase with the anode voltageof the other pair of valves. Thus, it will be seen that by varying themagnitude of this component voltage, the phase relationship of theresultant grid voltage, 1. e., the vectoral sum of the component voltageand the grid bias voltage, may be varied as desired with the result thatthe magnitude of the current supplied to the electric pilot motor 24 iscorrespondingly varied. It will also be seen that by reversing thepolarity of this component.

voltage and varying its magnitude, the opposite pair of valves will beenergized so as to supply a current in the opposite direction to theelectric motor. This reverse current also has a value dependent upon themagnitude of the component voltage. For the purpose of varying themagnitude of the component voltage supplied to the grid circuit of theelectric valve apparatus, suitable rotary induction apparatus isprovided. This rotary induction apparatus comprises the control deviceI5 and a similar device '31.

The control device l5 comprises a rotor member I50, provided with asingle circuit winding (not shown) and a stator member l5b provided eafl tnibut delpolynzireuitawindinatelnet: therehazprod einen;cheneeinthe-te ionat t e rs showmlwhiohsis physical-lygxshnilamtoa thre pulleymmg-The glevioe-iJ providedrioi; com per-1, phaseminding;eThjessingleicircuituroton:winding:l satingziorythisg11angein;tensionomprisesa is connectedito the upper.amiimiddlesupplylines pulleyetiamounted engagement Wibh :thefCaib1-Bg 3|.1iTIfe? devices31 is lin lall respects i idellticailmfi @so as tOTOtate-Withtheicalolewhen it is in motion; h with atheldeviceiiclfihitThelterminalssof :theistat-on' tog-etherza Worm 14 Mtfihfifid t r by f wwindingsof bothadevicesvlfi and 3:! :nrelconnectedh movingathe' positionof :the;.1:a segment Also together-by: means ofaconductors-:38sandtthersineh as to :change. the;;tensio nsetting ofthe; spring; 43 gle oircuit-rotor winding of-thei:devices!:is co ofltheltension responsive devi-e.e .---;Oloyious1y,;the;- nected to theprimary-winding of the transit l iiwormfli :might:bezdirectly'w netfiditov l ld lmsrformer iw- A reversingswitohing deviceo3931sl3liidesired. includedin v the connections for raversingthe Anelectromagnetically operated elinesswitoh All polarity of thecomponentvoltages-supplied to is provided for. establishingandinterrupting the the grid circuit of the'-eleeteic 'va1ve" apparatuspaware-connections for;the ,electric valveapparathereby providing forseleetive energization of 15a tus: e The energizing:circuitnof the lineswitch one or the other -ot-the pairscof valvesezliawand=-- M xiscontrolled \byua suitable switchingdevice 2 filwayruzl of courseforoperationof the pilotemotor l; a, and-thedrivingmeamdfl inthexiesiredmtire'c To plaoethe system incondition for operation, t me 7the handle of the control device I5 is turnedwto T p a y w d fl t e 7zgthe constant tension tie position as indicatedby Vice 1 5, whenenergized eprodudes an alternating- A thepOi11teI -&9 and 00- operatingdial 50.: c In this. magnetic field bymeansof whioh-avoltag-ee s iposition, -the. .axis of the -.magnetic field produced duced 'inthestator Windin ;-'t y g by- -the-=stator winding of the device -31 will.he

current to fl w in t e stato din sn f hwat rightangleswith-the axis oftherotorHwinddevice 31; This current inturn produces an al- 25.5:ing ofthe device -3'I..when the rider rolllll i in ternatingmagneticflfiel'drby S"' a position corresponding-With the tension thatvoltage-is induced in the rotor-winding of device t is d i e t holds 31when the relationship between -the axis Of" with; the foregoingunderstanding 9f the 3ptherotor, Winding-and the axis'of the maenetioparatus and; its -organization in the completedfieldisotherthan-90-e--Theretore when this-90 n ftem, the operation of thesystem itself will 1 r t s p b r p'volta eis d fl d iflihe readily ,beunderstood from thefollowingdetai-led a rotor winding andconsequently nocomponent description t p l t0 t s i i t id e- Assumingthat thehook-lfihas previously been trio v lv pp conditionsrtheh lowered to-a positionin which it can be inserted system is die-energized and-at-resta- 5amthe eye of the seaplane,-the-directional switch fl 39is operatedtotheupposition as indicatedancfpinionfll -'tot he cable tension'respfi 'd't viously been actuated to its 'closedposition to Vice illustrated as arider 1 p eyfiew complete, anenergi-zing circuit'for the operating i ten m h'fi b1e". byimfi i coil of the line'switoh M,"which is thereforeclosed a Sp 3:" "Therotor 10f the-devi t'l zeroed to complete-the powerconnection from the supplyso that'no-voltage-is induced in-thewotorwindlin'e 3|;to the electric 'valve ap aratus ing When 'p y 421s ina pfedet Y ifl *P =I" The hook 1 0 is inserted in the-eye of-the--seasition such'asthatin which it-isillustra-ted.-- lrr plane, byone of the-members of the crew- Unthis position; ;-a raeksegment' 144'?which includes '1 th se is quite calm while thisis taking place;the-support-for the-spring-43iremains in-a fixed: the seaplane will berising; and falling with' -the Position; Pulleyfi is d"-'into-:areuate13m". waves, After thehconnection hasb-eenmade-a tact-with the--cable by-the -force-rof the sprin falling wavegmotion causes the seaplane todrop a d" this f r s b l nc y f nsi n to a lower position-andthis ofcourse, willtend the cables" Whenpa seaplan'ero 't t s,fl to'increasethBtGIlSlOll in the'cable-causing the on-the surface of the'water; it s"fifi fied" y" riden-roll; 42 to'movetoward-the right toa posi-- th w v mt on ndii' "is ther re 3 66 5 3 28? tion in which the-horizontalcomponent of the tentha't thvcfi lebe' l ia'nd" u d."fi'q *tt sion willbalance the force Offiiliipiingi 4A's tlhe hoist h to take care 0f the?changein-positionw pider roll-QT-moyes tothgrig I 7 a rag a, so T e pnsive devicer43 is in t y moves to the right-causing- -the rotor of the.device calibrated-to'hoide tension--inthe caflole ll that-:131to-rotate.- Asa result of thisrotatiomtheaxis is less-tharrthe forceq-to =1ift-'*the-b0atof the rotor-wincling of the-device3l=is--r0tatedorseapla from the esurface'ofzthewatelt The" out-of the QO-"reIationship with-theaxis 0f the rack and pinion dl are "so" designedthat --t fieldof the-stator and-a voltage is induced in the rotor-memberof the-device -31 can--0nly--be"'r0-" rotor-windingw This---voltageisii'n-pressed asa tated through-a limited; ranger The reasonforcomponentvoitageonthe-grid or input-circuit ofthis isto"permit"the-speed oontrol-devioe5-to' the-"electricvalveapparatus;The-polarityof this energizethe systemand-increasethatensiondn;voltage-is such-as toadvancethephase-of the thecable beyond; the'valuewhich" the-constantgrid-vo1tage withrespectto the anode voltage oftenSiO pp s Set i' that 'b one-:of the pairs of valves-and toretardthe-grid or seaplane can; -be--raised from-"the surface of-- voltage ofthe other pair of-valvesi- It-is assumedthe water. that the'polalityofthisoomponentvoltage is such Maintaining constant tension" in-the1cable-at as to--advance thephase of the grid-voltageof the the point ofengagement witnthepulley fliwilh pair of valves--26apcausing-thispairotvalvesitot not insure constanttension at the point-of eonsupplywurrent-tothearmature of the pilot motor. nection of the cablewith"the -seap1ane;--i. e., -at 24. As a result of this, the pilotmotor24 is=enerthe. hook-i0. The difference between thehighgiZ-ed-and-rotatesthe inputshaft l8 and the pilot and low.positions-of the seaplane is-frequently so; shaft 20 in-such adirection-that the variable-sr eed great that a considerable weightofpableisreeled transmission :devicel4 drives the-drum 43: m -a on orofithe drum betweenthe'se two-positionsdirection-to-payoutcableandthenebyto reduoe decreased sufllciently topermit the spring 43 to restore the rider roll 42 to its originalposition in which the rotor winding of the rotary induction 3! is alsorestored to its original position in which no voltage is induced in therotor winding. This, of course, de-energizes the electric valveapparatus as well as the pilot motor 24. The output shaft 2| continuesto rotate only for the brief interval of time necessary for theconnections 20, 28, 30 to restore the control element 20 to its neutralposition.

When the wave motion causes the seaplane to rise to a higher position,the tension in the cable tends to decrease, allowing the spring 43 tomove the rider roll 42 to the left, which in turn causes a voltage to beinduced in the rotor windings of the induction device 31 of oppositepolarity. As a result of this, the opposite pair of valves 26b isenergized and current is supplied to motor 24 for rotation in theopposite direction, causing opposite rotation of the motor 24 andopposite rotation of the throttle shaft 20. As a result of this, theoutput shaft of the variable speed transmission device is driven in theopposite direction to reel in cable until the tension is increased tothein-ital value. When the initial tension is restored, the rider roll 42is returned to its initial position as is the rotor winding of therotary induction device 31 as a result of which the electric valveapparatus and the motor 24 are again de-energized and the output shaftof the variable speed transmission device I4 is again brought to rest.

As pointed out in the foregoing, maintaining the tension constant at thepoint of engagement of the rider roll 42 will not insure constanttension at the hook because of the changing weight of the effectivelength of the cable as it is unwound from the reel. As the cable is paidout from the unwinding drum, the tension in the cable tends to increaseowing to the increasing weight of the unwound cable. Since the tensionresponsive device is set to hold a constant value of tension at thepoint of engagement with the rider roll 42, it would function to reducethe cable tension which of course would result in reducing the tensionat the hook I!) which is not desired. However, as the cable is paid out,the pulley 45 is rotated in a clockwise direction, an amountproportional to the amount of cable paid out. The rotation of pulley 45causes segment 44 to move to the left to increase the tension setting ofthe spring 43. The tension responsive device will now function to hold ahigher value of cable tension at the point of engagement of the cablewith the rider roll 42 and this in turn functions to maintainsubstantially constant cable tension at the hook l0.

When the seaplane has finally been maneuvered into a position from whichit can be raised from the surface, the handle of the speed control device I5 is rotated to a position for hoisting at a desired speed asindicated by the position of the needle on the calibrated dial 50. Thetension responsive device, of course, always attempts to hold a constantcable tension, which is less than the force required to raise theseaplane from the surface. Therefore, in order to overcome the effect ofthe tension control so that the seaplane can be raised from thesurface-the rotor of the speed control device I5 must be rotatablethrough a greater angle.

Rotation of the rotor of the speed control device l5 to a predeterminedspeed position energizes the pair of valves 2% which supplies current tothe pilot motor 24 in such a direction that 8. the ensuing rotationmoves the throttle shaft 20 in such a direction as to cause the drum l3to hoist the seaplane. As long as the speed control device I5 ismaintained in the set position, the pilot motor 24 will continue torotate and the drum. l3 will be driven at a corresponding speed. Incontrolling the hoisting and lowering operations of the seaplane, thespeed control device l5 may be preset for a desired speed and the actualraising and lowering operation (depending of course upon the position ofthe switch 39) can be initiated by operation of the switch 48 tocomplete the supply connections from the supply line 3| to the electricvalve apparatus.

Although in accordance with the provisions of the patent statutes, thisinvention is explained as embodied in concrete form, it will beunderstood that the apparatus and connections shown are merelyillustrative and that the invention is not limited thereto, sincealterations and modifications will readily suggest themselves to personsskilled in the art without departing from the true spirit of theinvention or from the scope of the annexed claims,

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A control system for hoists and the like having a hoisting cable anda winding drum therefor comprising a tension regulator responsive to thetension in said cable at a point between said drum and. the attachmentof said cable to its load, a device for setting said regulator tomaintain a predetermined value of tension, and means for actuating saidtension setting device in accordance with the efiective length of saidcable thereby to vary the tension in said cable at said point so as tomaintain substantially constant tension in said cable at the point ofattachment to its load.

2. A control system for hoists and the like having a pulley, a windingdrum and a hoisting cable passing about said pulley to said drumcomprising driving means connected to said drum, a tension regulatorresponsive to the tension in said cable at a point between said windingdrum and said pulley for controlling said driving means, a device forsetting the tension to be maintained by said regulator, and means foractuating said setting device in accordance with the effective length ofcable unwound from said drum thereby to control said driving means tovary the tension in said cable at said point so as to maintainsubstantially constant tension in said cable at the point of attachmentto the load.

3. A control system for hoists and the like having a hoisting cable anda winding drum therefor comprising driving means connected to said drum,means responsive to the tension in said cable at a point between saiddrum and the attachment of said cable to a load for controlling saiddriving means, a device for setting said tension responsive means tomaintain a predetermined value of tension in said cable, and means foractuating said tension setting device in accordance with the length ofcable passing said tension responsive device thereby to vary the tensionat said point between said drum and said load so as to maintainsubstantially constant tension in said cable at the point of attachmentto said load.

4. In a control system for hoists and the like having a hoisting cableand a winding drum therefor, driving means for said drum comprising amotor and a variable speed transmission dc vice connected between saidmotor and said drum,

: -;fisai:d-.-=transmission -devicehav;ing a speed control- :-.;2ling.element, a. -.pilot motorz;- foractuating saidspeedmontrollingielement,.amanually presettable "deviceifor; controllingthe speed ofrsaid pilot motor thereby to. :control --the :speed of:said-drum; and mmeans actuated-by: the "tension of -said-cablefor--actuatingsaid-pilot motor to wmaintainathescable etensionsubstantially constant.

- 5-.@In a controt system-for .hoists and: the like -.-zhavinganhoisting cable-wand a winding-drum therefor; aw-motorwanda-zvariablewspeed:transmission; device connecting said motors-and said idrumr isaid transmission device having arlspeed controlling element, a?pilot motor-:for- "actuating saidw'element; means =forrmaintaining:substantiallyrrconstant cable-tension zcomprising :a-eride'r roll:actuated byrsaid :cable andtha-ving limited r range of movement:andia-rotaryinduction device 1; actuated by.said'rider-lroltfor-*controlling-the en- :grgization. of saidpit":'.m0tOl':, :andmeans for, controllingrthe hoistingspeed ofsaid-cable-eom rap-rising a manually pre'settabl-e .TOtfily-h inductiondevice for controlling the speed ofesaid' pilot motor.

6. In a control system for hoists and the like having a-hoistingncablezland a winding drum rtherefor, drivingmeanghayinganoutput shaft connected to said drum, an input shaft,,a speed controlelement and a differential device connecting said output shaft, inputshaft and control ele; mentso that the controlelement is actuated towproduce a speed of said output shaft proportional to thexspeed of saidinput shaft, a pilotimotor for actuating. said speed controllingelement; :means wrrlIQSPQDSiVE to the tension. ofvsaid cablerfor en tieerg-izinglsaid pilot motorto actuate said driving nil-means to-maintainsubstantially constant cable ..=tension,..and means for efieotingoperation of said :snpilottmotor at a selectedspeed thereby. to ef- -efectoperation of said cablev at a corresponding \pspeed.

e. 7a In ,aacontrol system ,for. hoists andthe like Mhaving hoistingcable. and a winding drum .,therefor, driving means having an outputshaft connected to said drum and a directional control element, wpilotmotor --foractuating said element, a controldevicerforsenergizing-saidapilot :rcmotor to elfect operation ot-saiddriving means in eithers'directi-on, andrmeanszresponsive to tensessionin-;said cableaforeenergizing said: motor to control said driving meansto maintain substantially constant cable tension.

8. In a control system for hoists and the like having a hoisting cableand a winding drum therefor, driving means for said drum having a 55speed control element, an electric motor for actuating said speedcontrol element, electric valve apparatus for supplying said motor,means responsive to tension of the cable for energizing said valveapparatus thereby to energize said pilot motor to control said drivingmeans to maintain substantially constant cable tension, and additionalmeans for energizing said valve apparatus to cause said motor to controlsaid driving means to operate said drum in a selected direction.

9. In a control system for hoists and the like having a hoisting cableand a winding drum therefor, driving means for said drum, said drivingmeans having a control element, a pilot motor for actuating saidelement, electric valve apparatus for supplying said motor, a deviceresponsive to tension in the cable and a rotary induction deviceoperable thereby through a limited range for energizing said valveapparatus, to con- 72 10 trolsaid :driv ing means to maintainsubstantially 1aconstant-cable+.tension, and a:ma n,ually preset- I :rstable, rotary. rinduction device aoperable through arelativelylargerrangetthanthe. range of. said 5 'first. mentioned. -inductiondevicetfor. controlling 5 E.saio'l; valve: apparatus torenergize,lsaidnpilot: mot rll). In .a.lcolntrol-system-for hoistsnand the likewhaving a-lioistingcable-sand a w inding drum therefor, drivingmeansfonsaid drumlhavin a -c0ntr01--element, .a pilotmotor-aforactuating said el-element, means for. supplying.- said, motor.com-

pr-isingmelectric. valve lapparatusf-provided with man o.utput-circuit..and-:with an inputcontroL-cirt-cult, -a-device-dor-controllingthe.voltage of. said 1;- i-nput circuit thereby to control .energization of-..-saidmotor andpperation of .said drivingmeans, wand. means forcontrolling the-.tension on said i :cabletcomprisinga-device:movab1e in.response to {variations in;- the -.tension, .and .avoltage. controlt-device in circuit with said first mentionedlvolt-;-;age.controldeviceand actuated by movement of aesaid.tensionresponsivedevice forcontrollinglthe -tvoltage of-said input circuit.

11.-. Inacontrol. system forlhoists andlthe like ehaving a shoist ingscableaand a winding drum therefor; driving emeansaconnected to saiddrum, -saiddrivin means-having :al-controlrelement, a pilot ImOtor,.--for (actuatingsaid. element, supply r meansafors said lmotoricomprising. electric. valve -rapparatus. provided with a,---c0ntrolgrid, ..ineans "for 1 controlling the tension ofsaid, .cablehcomrisingar-ider roll movable inresponse to changes in thetension ofs-ther-cablearrd agridwoltage acontrol -device -actuated-ather ebyrfort energizing:said valve-apparatus and motor and a manually =operable: grid. ivoltagecontrol,- device in circuit with said-v first --mentioned grid voltagecontrol device foreffectingenergization of said lvalveapparatus andsaidmotor .thereby to :effect operation of saiddriv-ingmeans. a

i 1 12;. In at control systemfor=hoists--and-thelike ehav-ing ahoisting? cable.' and a: winding drum therefor, driving means connectedto said-drum, .u saiddrivingemeans having anelement for con--trolling-direction.and speed apilot IIlOtQIgfOI ac- -,-,t.uating:.said:element -means :zfor controlling 13116 direction-andspeed of saiddriving'meanstcom- A ,prisinglelectric -vaWaaDPmatuslprovidedwith an (1anode; and a! control -grid,-;means. ion/supplying 5 alternatingnvoltagesf to, said grid and lanode, a manually presettable device forvarying the phase relationship between said grid and anode voltagesthereby to energize said motor and effect operation of said drivingmeans in a selected direction, and means for controlling the tension ofsaid cable comprising a rider roll movable through a limited range and aphas shifting device actuated thereby and in series relationship withsaid first mentioned phase shifting device for controlling theenergization of said valve apparatus.

13. In a control system for hoists and the like having a hoisting cableand a Winding drum therefor, driving means connected to said drum, saiddriving means having an element for controlling speed and direction, apilot motor for actuating said control element, means for controllingthe direction and speed of said motor comprising electric valveapparatus provided with an anode and with a control grid, means for sup-7 plying alternating voltages to the grid and anode, and means forcontrolling the tension of said cable comprising a resiliently mountedrider roll movable through a limited range in response to tensionchanges and a rotary induction device actuated thereby for varying thephase relationship between said grid and anode voltages to effectenergization of said motor and operation of said driving means, andmeans for efiecting operation of said driving means at a selected speedcomprising a presettable rotary induction device connected in seriesrelationship with said first mentioned rotary induction device andoperable through a relatively larger range than said first mentioneddevice.

14. In a control system for hoists and the like having a hoisting cableand a reel therefor, driving means for said reel having a controlelement, 'a pilot motor for actuating said element, electric valveapparatus for supplying said motor, means for maintaining the tension ofsaid cable substantially constant comprising a 'device movable inresponse to changes in tension of said cable and means actuated therebyfor controlling said valve apparatus to control said driving means, andmeans for varying the setting of said movable tension responsive devicein accordance with the amount of cable unwound from the drum thereby tomaintain substantially constant cable tension at the point of attachmentto the load.

15. In a control system for hoists and the like having a hoisting cableand a winding drum therefor, driving means connected to said drum, saiddriving means having a control element, a pilot motor for actuating saidelement, supply means for said motor comprising electric valve apparatusprovided with an output circuit connected to said motor and with aninput control circuit, means for controlling cable tension comprising arider roll movable in response to tension changes in the cable and adevice actuated thereby for controlling the voltage of said inputcircuit, said rider roll being provided with a spring for holding it inengagement with said cable, and means for compensating said tensiondevice for the length of cable unwound from said drum comprising aroller actuated by the motion of said cable for varying the tension ofsaid spring. I

16. A control system for hoists and the like having a hoisting cable anda winding drum therefor, controllable driving means for said drum,control means responsive to the tension in the cable at a pointintermediate the drum and load for maintaining the tension in said cableat the point of attachment to its load substantially constant, and meansfor varying the setting of the tension responsive means in'ac'cordancewith the length of cable unwound from the'drum.

17. A control system for hoistsand the like having a pulley, a windingdrum and 'a hoistin cable passing about said pulley to said drum,controllable driving means for said drum, control means responsive tothe tension in the cable at a point intermediate the drum and pulley formaintaining the tension in said cable at the point of attachment to itsload substantially constant, and means for varying the setting of thetension responsive means in accordance with the length of cable unwoundfrom the drum.

18. A control system for hoists and the like having a hoisting cable anda winding drum therefor, controllable drivin means for said drum,control means for maintaining the tension in said cable at the point ofattachment to its load substantially constant, and means for varying thesetting of the tension responsive means in accordance with the lengthofcable'unwound from the drum.

MARTIN A. EDWARDS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,049,826 Dunlop Jan. 7, 19131,433,079 J ett Oct. 24, 1922 1,773,709 Daniels Aug. 19, 1930 1,804,945Miller May 12, 1931 1,815,100 Francis July 21, 1931 1,832,430 Siebs Nov.17, 1931 1,857,817 McCann May 10, 1932 1,902,972 Rouse Mar, 28, 19331,966,214 Palmer July 10, 1934 1,976,611 Gulliksen Oct. 9, 19342,024,708 Staege Dec. 17, 1935 2,032,176 Kovalsky Feb. 25, 19362,163,231 Smaltz et al. June 20, 1938 FOREIGN PATENTS Number CountryDate 10,361 Great Britain 1915 176,324 Germany Oct. 11, 1906 300,064Great Britain Nov. 8, 1928

